Tile drain ... Scanned 2005 for the 75th anniversary exhibition and publication. 411 Horizontal (normal) ... July 1947
Notebook ... Arthur W. Parsons, Margaret Crosby ... 401 599 ... 1947
ΠΠ-3 410, 411 Section ΠΠ 73 Section ΠΠ 74 Section ΠΠ 75 Section ΠΠ 76